1. Field of the Invention
This invention relates to an elevating device such as a goods or passenger lift or elevator which is particularly although not exclusively suitable for installation in low rise residential buildings.
2. Background Discussion
Conventional lifts or elevators for medium to high rise residential or office buildings generally comprise a car suspended by a block and tackle mechanism and controlled by an electric hoist. In medium rise buildings the car may be moved up and down by an extensible hydraulic lift mechanism situated below the car. In both cases, the lift well must be formed as an integral part of the building structure during construction. With the former type of lift, a winch room must be provided atop the lift well to house the hoist mechanism and with the latter a deep well must be provided to house the hydraulic hoist apparatus. Stringent safety regulations applied to such lifts or elevators impose severe design constraints on their construction, making them uneconomical in buildings of less than say, five or six floors. A further disadvantage of these types of lifts or elevators is that generally it is not possible to retrofit such apparatus to existing buildings due to structural limitations or prohibitive cost considerations.
In an endeavor to overcome the above problems and to provide a lift or elevator structure for low rise buildings of say, two to four floors, it has been proposed to provide a screw-driven lift or elevator. In such a structure, the car is mounted for sliding movement on a pair of tracks spaced at a width approximately that of the car. The tracks are generally U-shaped channel sections and they accommodate rollers mounted on each side of the car adjacent both the top and bottom of the rear wall of the car. The elevating mechanism comprises either a driven helical screw with a fixed nut attached to the car or vice versa.
Although these screw-driven lifts or elevators are generally satisfactory in operation they nevertheless suffer certain disadvantages. The main disadvantage is the cost of installation due to the problems of mounting the spaced parallel roller guide tracks, particularly when such an apparatus is being retrofitted to an existing building. For this type of lift, the tracks must extend to the full height of travel of the lift, i.e., at least to the ceiling of the first floor in a ground to first floor elevation. Another main disadvantage is the lack of flexibility in mounting of the apparatus. A continuous wall structure is needed behind such screw-driven lifts or elevators in order to mount the tracks thereto. In addition, considerable space must be provided between the support wall and the rear wall of the car to locate the helical screw drive mechanism. Space must also be provided beneath the floor of the car to accommodate the screw/nut drive mechanism when the car is fully lowered. Other disadvantages are that access to or from the car is not possible from the rear of the car due to the configuration of the tracks and further, space must be provided to enable the guide tracks to extend to the full height of travel of the car.
A significant disadvantage of prior art small elevators used in residential situations relates to their control mechanisms. Lifts of this type powered by mechanical and/or hydraulic means have an instantaneous stop and start control mechanism. Starting and stopping of the lift car is accompanied by a jerking motion and often an audible "clunk". The lack of smooth, silent operation normally associated with this type of lift in a large office building can engender a feeling of insecurity in a passenger, particularly a nervous person or an elderly or infirm person.
Prior art personnel elevators are described in Australian Pat. Nos. 408,046 and 446,606. Other hoisting mechanisms of various kinds embodying a columnar support similar in principle to the present invention are described in Australian Pat. Nos. 153,308, 153,364, 219,658 and Australian Patent Applications 1926/21, 14680/70 and 37523/78.